1. Field of the Invention
The present invention relates to fluid handling apparatus, and more particularly to marine tanker loading arms with systems for counterbalancing the arm members.
2. Description of the Prior Art
Various types of fluid transferring devices are used in conveying fluids between a dock, buoy, or floating barge and a tanker or other marine transport vessel. Some of these devices are large articulated pipe structures referred to as marine loading arms, such an arm generally comprising an upstanding support riser on which is pivotally mounted an assembly of two or more arm members that are pivotally interconnected by swivel joints in a manner to allow the arm to accommodate itself to the movements of the buoy, barge and/or tanker while fluid transfer is in progress. Some examples of these earlier fluid transferring devices are described in U.S. Pat. Nos. 2,980,150, 3,382,892 and 3,805,834 to Bily, U.S. Pat. No. 3,581,769 to Haley, U.S. Pat. No. 3,889,728 to Riche, and U.S. Pat. No. 4,252,162 to LeDevehat.
It is common practice to install weights to counterbalance a loading arm about its horizontal pivot axis at the riser so that it can be more easily maneuvered. To achieve a balanced condition, some marine loading arms are provided with a support beam that is secured to the inner arm member and extends rearwardly therefrom behind the riser, and with a counterweight fixedly mounted on an inner sheave that is rotatably mounted on the support beam and connected by an endless cable to an outer sheave located at the juncture of the inner and outer arm members. The outer sheave is fixed to the outer arm member but rotatable with respect to the inner arm member, so that the counterweight, sheaves and cable function as a system to counterbalance the inner and outer arm members in all operating positions.
Although marine loading arms generally function satisfactorily, one of the problems sometimes encountered in their use is the difficulty associated with connecting them to a tanker or other vessel when they are in an unbalanced condition. Another problem is that some marine arms, when in either an over-balanced or under-balanced condition, have a tendency to move dangerously close to the tanker, and thus present a risk of impact or collision therewith, when they are disconnected from the tanker's manifold under emergency conditions. A further problem with some loading arm is that the curved path followed by the connection assembly at the outer end of the arm, when emergency disconnection is effected, sometimes results in collision between the arm and tanker, especially when the angle defined by the inner and outer arm members remains constant or changes too slowly after disconnection occurs.